Much of the current activity in the dot matrix print head industry is being directed to improving the printing speed (characters per second, lines per minute) of the head to meet the needs of large company users. Such increased printing speed is usually accomplished with little thought being given to and at the expense of ease of manufacture, cost, reliability, ease of repair, degree of training needed to perform repairs, ruggedness, long life, and cost-performance ratios. Often, these current print head designs require the use of expensive and sophisticated materials and technology such as tungsten print wires, synthetic ruby bearings, and powdered metal technology with its expensive and scarce blends.
In direct contrast to the high speed printing needs of large company users are the needs of the rapidly developing personal computer market and small business computer market. In the personal and small business computer markets, the printing speed of the head is of relatively minor and secondary importance in comparison to cost, reliability, ruggedness, long life, ease of repair, and the degree of training necessary to perform repairs. It was with these needs of the personal and small business computer markets in mind that the present invention was developed. In contrast to the expensive and somewhat exotic manufacturing technique used in making most of the current print heads (e.g., powdered metal technology, tungsten print wires), the present invention uses simpler stamping and screw machine technique, cheaper materials such as steel print wires, and greatly simplified manufacture and assembly procedures including the use of assembly aids for inserting the print wires into spaced-apart guide members, a grinding aid and method whereby all of the print wires can be more easily and quickly ground to the proper length, and unique coil assembly and mounting plate designs whereby the clappers or armatures are automatically aligned with the impact ends of the print wires during the assembly of the print head.
Illustrative of the state of the art in dot or wire matrix print heads are the following U.S. Pat. Nos.:
3,333,667: Nordin PA1 3,467,232: Paige PA1 3,828,908: Schneider PA1 3,842,955: Iwasaki PA1 3,854,564: Flaceliere et al PA1 3,889,793: Cattaneo PA1 3,896,918: Schneider PA1 3,897,865: Darwin et al PA1 3,929,214: Hebert PA1 3,991,869: Berrey PA1 3,994,381: Hebert PA1 4,004,671: Kondur, Jr. PA1 4,004,673: Burzlaff et al PA1 4,009,772: Glaser et al PA1 4,049,107: Murat PA1 4,049,108: Giessner PA1 4,051,941: Hebert PA1 4,060,161: Nelson et al PA1 4,079,824: Ku PA1 4,081,067: Schrag et al PA1 4,091,909: Lee PA1 4,117,435: Hishida et al PA1 4,135,830: Hishida et al PA1 4,140,406: Wolf et al PA1 4,141,661: Geis et al
None of these patents, however, discloses the unique features of the present invention nor do any of these prior patents meet the needs and requirements of the developing personal and small business computer markets as well as the present invention.